In the foundry industry, one of the procedures used for making metal parts is by sand casting. In sand casting, disposable molds and cores are fabricated with a mixture of sand and an organic or inorganic binder. The binder is usually used to strengthen the cores, which are the most fragile part of the mold assembly.
One of the fabrication processes used in sand casting is the cold-box process. In this process a gaseous curing agent is passed through a mixture of the sand and binder to cure the mixture.
A binder commonly used in the cold-box fabrication process is a polyurethane binder derived from curing a polyurethane-forming binder composition with a gaseous tertiary amine catalyst. The polyurethane-forming binder composition usually consists of a phenolic resin component and polyisocyanate hardener component which may react prior to curing with the gaseous catalyst. If this reaction occurs, it will reduce the flowability of the mixture when it is used for casting, and the resulting molds and cores will have reduced strength.
The bench life of the mixture of the sand and polyurethane-forming binder composition is the time period between forming the mixture of the sand and polyurethane-forming binder and the time when the mixture is no longer useful for making acceptable molds and cores. A measure of mold and core acceptability is tensile strength. If a mixture of sand and polyurethane forming binder composition is used after the bench life has expired, the resulting molds and cores will have insufficient tensile strength.
Because it is not always possible to use the mixture of sand and polyurethane-forming binder composition immediately after mixing, it is desirable to prepare mixtures with an extended bench life.